Global warming affects caribou diet, rabbit camouflage and more

By Livia Albeck-Ripka and Brad PlumerThe New York Times

Sunday

Apr 15, 2018 at 5:00 AM

Every year, as the seasons change, a complex ballet unfolds around the world. Trees in the Northern Hemisphere leaf out in the spring as frost recedes. Caterpillars hatch to gorge on leaves. Bees and butterflies emerge to pollinate flowers. Birds leave the Southern Hemisphere and fly thousands of miles to lay eggs and feast on insects in the North.

All of these species stay in sync with one another by relying on environmental cues, much as ballet dancers move to orchestral music.

But global warming is changing the music, with spring now arriving several weeks earlier in parts of the world than it did a few decades ago. Not all species are adjusting to this warming at the same rate, and, as a result, some are falling out of step.

Scientists who study the changes in plants and animals triggered by seasons have a term for this: phenological mismatch. And they’re still trying to understand exactly how such mismatches — such as the blooming of a flower before its pollinator emerges — might affect ecosystems.

In some cases, species might simply adapt by shifting their ranges, or eating different foods. But if species can’t adapt quickly enough, these mismatches could have ‘‘significant negative impacts,’’ said Madeleine Rubenstein, a biologist at the U.S. Geological Survey’s National Climate Change and Wildlife Science Center in Reston, Virginia.

Here are some examples of mismatch that scientists have discovered:

•An orchid's sex life

The early spider orchid relies on deception to reproduce. Each spring, the orchid, whose bulbous crimson body looks like an insect, releases a pheromone that tricks solitary male bees into thinking the plant is a mating partner — a key step for pollination.

This ruse works because the orchid tends to bloom during a specific window each spring — shortly after lonely male bees emerge from hibernation but before female bees appear.

Yet with spring coming earlier, female bees are now emerging sooner and luring the male bees away from the lovelorn orchid, according to a 2014 study from Britain.

By examining data collected in herbariums and in the field over a century, the researchers found that the gap between the times when male bees and female bees emerge shrinks by about 6.6 days for each degree Celsius of warming, giving the orchid less opportunity to reproduce.

•Too close for comfort

Climate change doesn’t just cause missed connections. In some cases, the advance of warmer weather can lead to perilous meetings.

In Finland, for example, the Northern lapwing and Eurasian curlew have usually built their ground nests on barley fields after farmers have sown their crops in the spring. But as temperatures have risen, the birds are now increasingly laying their eggs before the farmers get to the fields, which means their well-concealed nests are more likely to get destroyed by tractors and other machinery.

Looking at 38 years of data, researchers found that farmers in Finland are now sowing their fields a week earlier in response to warmer temperatures, but the birds are laying their eggs two to three weeks earlier. The response is a decline in the birds.

•Late for lunch

Caribou in western Greenland follow a strict seasonal diet. In the winter, they eat lichen along the coast. In the spring and summer, they venture inland to give birth to their calves and eat the Arctic plants that grow there.

As Greenland has warmed up and sea ice has declined, however, those inland Arctic plants have been emerging earlier — with some plant species now greening 26 days earlier than they did a decade ago. But the caribou have not shifted their migration as quickly. And scientists have documented a troubling trend in the region: More caribou calves appear to be dying early in years when the spring plant growth preceded the caribou’s calving season.

Though the study found a correlation only between warmer weather and caribou calf deaths, "‘it’s consistent with the idea that mismatch is disadvantageous," said Eric Post, an ecology professor at the University of California, Davis. When Arctic plants green up earlier, they might become tougher and less nutritious by the time the caribou get there and start eating them.

•Wardrobe malfunction

Climate change doesn’t just cause mismatches in the spring. Consider the snowshoe hare, whose fur coat has evolved to change from brown to white during the winter for camouflage. As the Earth has warmed, however, snow cover in the hare’s habitat melts sooner, leaving the animal more exposed to predators.

"Camouflage is critical to keep prey animals alive," said L. Scott Mills, a professor of wildlife biology at the University of Montana who studies the impacts of camouflage mismatch on species such as the snowshoe hare.

For every week the hare is mismatched, Mills and his colleagues found, it had a 7 percent higher chance of being killed by predators.

Currently, the hare is mismatched by about a week or two. But by mid-century, Mills said, that could extend up to eight weeks. If that were to happen, he said, the hare ‘‘would start declining toward extinction.’’

There is some good news for the snowshoe hare, however. Where evolution was previously thought to take millions of years, scientists now think an animal such as the hare could adapt in five to 10 generations, especially if those parts of the hare population that are more adaptable are protected.

"It does give us an avenue for hope," Mills said. "It’s not a foregone conclusion that species with phenological mismatch are going to go extinct."

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